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lurking_giant writes "In a report on NewScientist.com, researchers working on development of a space elevator (an idea we have discussed numeroustimes) have determined that the concept is not stable. Coriolis force on the moving climbers would cause side loading that would make stability extremely difficult, while solar wind would cause shifting loads on the geostationary midpoint. All of this would likely make it necessary to add thrusters, which would consume fuel and negate the benefits of the concept. Alternatively, careful choreography of multiple loads might ease the instability, again with unknown but negative economic impacts."

Especially since Kim Stanley Robinson wrote his "Red Mars" series & specifically addressed these issues. He correctly identified the problems, and came up with very realistic solutions.

Yes, the orbital section had to have thrusters to combat what is mentioned in the article.

He also determined that the 'elevator' portion would require significant advances in materials, and require a futuristic substance that could withstand the sheer loads & twisting due to wind, atmosphere, etc.

ACC?... served in the Royal Air Force as a radar instructor and technician from 1941-1946, proposed satellite communication systems in 1945[4][5] which won him the Franklin Institute Stuart Ballantine Gold Medal in 1963.

If the reason for coming with such a thing as a space elevator(which I agree is pretty impossible with any material currently known) is to cut down on the cost of getting things into space then why hasn't anyone been looking to build a "supergun" like Gerald Bull [wikipedia.org] had experimented with ages ago? It just seems logical that if you built it at the equator you could cut down on fuel required by using a gun style launch and then having the thrusters kick in at the top of the arc and use the momentum to assist getting the vehicle into space. And if we could build it as a magnetic coil or rail gun we could save even more by using electricity, which is easier to produce, than chemical engines.

So is there anyone looking at the "supergun" concept? or did the idea die out with Bull?

The space gun concept would really only be good for a very narrow range of payloads that can withstand the extreme g-forces produced by such a device. You can reduce the g-forces by using a longer barrel but it's still a concept that really isn't feasible.

What we should be looking at is a Space Fountain [wikipedia.org]. Yes, it seems like a very odd idea but it's backed by a lot of very good science and a lot of people are saying that it can be done with present materials and technologies. At the very least we should be experimenting with them on a smaller scale, using them to erect temporary masts and towers.

People who don't know, or who refuse to accept that things are 'imposible'. They're the ones who drive progress. Think the Wright brothers, Einstein or better still Michelangelo, who imagined flying machines and submarines that were only inviable because the necessary technology (engineering & materials) were not available.

After all, geosync orbits were thought up by first by a scifi writer...but to your point, Arthur C. Clarke did have a good grasp of Physics...

I know you were joking, but I really think it won't work for reasons not specified in the article. It's such a simple reason that I can't believe it's so rarely mentioned or addressed.

The earth is built very much like a capacitor. The ground has a fairly strong positive charge and the ionosphere has a fairly strong negative charge, with an insulating layer of air in-between. Carbon nanotubes can conduct electricity; so can most other materials I have heard of that would be used for a space elevator. I imagine that any conductor (and possibly dielectrics also when you consider electrical breakdown and the sheer current involved) would vaporize as soon as this circuit is closed. Coriolis forces and weight distribution and whether thrusters would be necessary seems trivial by comparison.

So use the current flow. You're breaking the earth's magnetic field lines with the cable. Not a lot of field strength, but it's a lot of field, sounds like a generator to me. Ship up the necessary kilograms of (i don't know, zinc perhaps) sacrificial anode and dump the potential via ions accelerated as lateral thrusters running continuously, and vary the flow in any particular direction to adjust the position of the cable terminus. The spare current could run the elevator cars.

With my luck, I'd get halfway up the space escalator and drop my luggage. It would thump its way down to with me running after it. It was embarrassing enough at the Aukland airport having everyone watch me put on a show, but to have it happen in front of half a continent, argh!

In all seriousness, the space elevator gets a lot of press because it's the concept that is easiest for the average person to understand, that doesn't mean it is the only option (or even the best option) to efficiently get stuff into orbit without rockets. I always thought the launch loop made more sense (http://en.wikipedia.org/wiki/Launch_loop/ [wikipedia.org]).

The idea is that the moving parts are what keeps the structure stable, rather than tension or compression. In theory it could be built with today's materials and technologies and could be cabable of launching more into orbit in its first month than has been launched to date with conventional rocket launches.

Then of course, there are the non-traditional rockets such as laser propulsion, where a laser is shined up from the ground to superheat the air in the rockets cone, which, in turn, produces thrust. And of course, my personal favorite, there's always Project Orion. Not the wimpy one NASA is using to get to the moon, I'm talking about the original Project Orion. As in, using thermonuclear bombs to launch a city sized spaceship into orbit.

The catapult is not even remotely the same as a launch loop. In the case of the catapult, all the energy is delivered from the power supply to the payload at once, and over a very short distance. A launch loop uses its power supply to maintain a loop of masses flying from one end to the other, and adds only minimal energy to each one on each pass. The payload then couples into this giant flywheel. This spreads the load on the power supply out, and also lets the payload take a *much* longer time to accel

Pendulums reach maximum velocity at the lowest point, not coincidentally where the atmosphere is thickest. Basically exactly the opposite of what you want, for values of "want" that don't include burning up.

Aside from that, swings/pendulums only work when the material holding the bob is relatively massless, otherwise you'd get massive oscillations that would rip the "ropes" free of their pivot, if you could even get it swinging at all.

But if we're submitting our votes for things that will never work, I vot

Speaking of which, there is an airship to orbit concept that was discussed here a few years ago.

You have two airships, a ground ship and an orbital ship. You put your payload on the ground ship where it ferried to a high altitude rendezvous with the orbital airship. The orbital airship raises the payload farther, to the highest point it can on buoyancy. That point is far below orbit, but the atmosphere there would be thin enough to permit the use of ion thrusters. Ion engines take the airship to orbit: a two week process. To return payloads from orbit the process is reversed.

Personally, I don't think this would ever prove to be practical, but it is possible to imagine it working.

The outfit behind this concept (JP Aerospace [jpaerospace.com] seems to be a volunteer organization of high altitude balloon enthusiasts. They've done a number of spectacular balloon missions, in one case sending a balloon to over 19 miles, or 1/3 of the way to the official "space" line. They don't seem to have done anything in the last year though.

Ahhh.... I see you've read the Red Mars trilogy where exactly that happened (albeit on Mars not the Earth.)

I always thought the space elevator seemed impractical. First there's a LOT of material needed to create the cable. Than there's the problem of "lowering" that massive cable to the ground. And of course it's vulnerability to shifting; half the time we can't even keep our satellites in the sky - how could we guarantee a cable would stay there?

There is no corresponding example of super-luminal travel. It is not possible given the current knowledge of physics, and that knowledge has been stable for a century. You are as likely to see violations of conservation of energy, or momentum, or baryon number (this is the one that nixes star-trek transporters) as you are a violation of the speed of light in vacuum.

The engineering required for this elevator is mind boggling. After witnessing the amount of time and effort that went into
a small suspension bridge spanning the river Thames in London (The Millenium Bridge [wikipedia.org]), the mere idea of this elevator scares the shit out of me.

I'm not saying it shouldn't be done. I guess my point is that the Millenium Bridge is so simple by comparison, yet it needed ~2 years of repairs after opening because of a wobble. People could have been thrown into the Thames, but no big deal, I guess. The space elevator, however, seems so much more prone to failure and with much bigger consequences.

We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too.

The engineering that was required for the Apollo missions was mind-boggling too, especially when you consider they were using computers back then less powerful than a typical scientific calculator, and didn't have much of our advanced materials science. Regardless, they managed to send people to the Moon many times, without any loss of life, and only one incident (13) which didn't result in any casualties.

I don't think they ever sent and cosmnauts into deep space, I know a fre unmanned spacecraft missed the moon but nothing manned. Of course if you happen to know otherwise I would love to hear from you.

I see you made it through two sentences in the summary. How about trying to read the third? "All of this would likely make it necessary to add thrusters, which would consume fuel and negate the benefits of the concept."

The coriolis effect is not a real force. It's an illusionary effect that happens when you have a moving point of reference. As to solar winds and stuff; can you be a little less vague. Let's say for a 10 meter thick cord, white color, how much force would be imparted on the cable over its length? Is the concept currently economical? No, and that's hardly news. Is it unstable and unworkable? Well... if you're pinning your conclusions something that doesn't actually exist to answer that, I think you might have a problem.

You are right, but you are wrong. The Coriolis effect is very real, but it is not force in the strict sense.

The gist of the point in the article is that as a payload is moved up the elevator, it must be accelerated to the side, since the upper portions of the elevator are moving circumferentially faster than the lower portions. The force required to accelerate the payload must come from the elevator itself, causing small displacement of the elevator. The use of the term "Coriolis effect" is not strictly wrong, though it is somewhat sloppy.

It doesn't really matter if it's a "real" force or not, the effect exists.

If you're sitting at your desk, and someone asks if you're moving, what's your answer, yes or no? If you say no, they'll agree with you, but you'll be wrong, because in reality you're moving as the Earth's surface spins in orbit, and you're moving even more since the Earth is orbiting the Sun, and then there's movement from the solar system moving through the galaxy. But if you bring this up in conversation, people will just think y

Damn Straight! This kind of instability is something that has been found and defeated many times before, particularly in Aerospace.

The Rocketdyne F-1 engines on the first stage of the Saturn V had a similar problem early in development. They had a nasty tendency to ring like a bell until they disintegrated (being very loose with this description for the sake of illustration). And they fixed it. The end design was incredibly stable and self damping. With little more than pluck, slide rules, and raw engineering talent. Hell, the entire computer facilities available to NASA at the time (late '50's to early '60's) were less than are available on any engineers desk today.

Solving supersonic flight was another issue of instability. The planes had a tendency to shake themselves apart. We solved that one with essentially no computer help at all (late 1940's).

I have confidence that this problem is solvable. It may not be easy, and may take some genius, but it is solvable.

Nobody said this would be easy (quite the opposite), and nobody is claiming we're even close to being "there" yet. But is the space elevator dead? No. Just still working out the kinks. Look, have you any idea of the number of launches required to prepare, by tiny increments, for the eventual (and still debated, snicker) moon landing? We'll get there, eventually.

Even with thrusters, it's bound to be a better long-term solution than rockets. Especially using ion drives, you could hard-wire the fuel supply from down below, so to speak, and so not need to haul that mass, too.

Ion drives need physical fuel as well as power... they just are a lot more efficient than traditional chemical-reaction drives. This is because they accelereate the fuel to near-lightspeed, maximizing the reactionary force per kg of fuel. (force is a combination of the mass expelled and the speed of which it is expelled... the faster the exhaust, the higher energy per kg of exhaust).

So, you'd still have to haul up fuel, just not as much as with chemical rockets.

In that novel he proposed timing the departures of loads for a space elevator on Mars. Not to damp oscillations, in this case, but to cause them. By timing the oscillations correctly, the elevator would oscillate out of the way of the moon Phobos, which orbits lower than the Martian geosynchronous orbit.

When it came down to it the space elevator though nice, is a dumb idea. Like the jet pack.
Think if the resources needed to defend it from terrorists, or maintenance costs. Seemed also like a put all your eggs in one basket as well
I mean we would be much better off to just improve our propulsion ability.
Personally i like a rocket powered mag-lev launch vehicle, that would travel down a rail that ends up pointing to the sky.

Just the opposite, actually. The jet pack is closer to what we're doing with space right now, which is strapping huge rockets on a much smaller payload. The space elevator would allow us to use whatever energy source we want to use to get the payload into space (still a significant amount of energy). In addition, it would provide a possible electrical line for electricity to go from space to the earth.

Arguing about protecting it from terrorists is, in a word, retarded. There's no reason that it will be a

Their big objection seems to be not that the forces on the elevator are unmanageable but that oscillation could lead to payloads being released into orbits that are "10 km" too high or too low, or that the oscillation could put the elevator in the path of a satellite. Correcting that would require thrusters.

For the first, surely you could simply time your release with the oscillation, to get into the orbit you want. Even if you couldn't, the space elevator would be good for putting things in geosynchronous or interplanetary transfer orbits. The cost of a bit of propellant to correct a +- 10 km error is pretty minor compared to getting into one of those orbits in the first place.

For the second, thrusters to purposely oscillate the cable to allow it to dodge out of harms way are a pretty standard part of any space elevator proposal. That is, the ability to move the cable a little is a desired, even necessary part of its design.

I agree with your assessment of their stated problem, but I'd like to know where they got that idea in the first place. Launching directly from the space elevator has never (in my understanding) been part of the concept. Instead, cargo (+ people) is offloaded at a station and is moved into a shuttle. The shuttle detaches from the station and then applies a thrust vector to move away.

The point of a space elevator is not to launch items directly into space, but to create a more efficient, higher through-p

just imagine the damage it might cause if the thing were to collapse and land over a populated area.

Depends on how you build it. If you're using carbon nano-tubes, then not much at all. Basically, much of it would go into space, a lot would get burned up on the way down, and the rest would be light enough that it's be more like a bunch of paper floating to the ground instead of a giant steel structure falling down. If it's heavy enough to cause damage, it's probably not going to be a good material to make the elevator out of in the first place.

Well, first you have to remember that if it fell, it would only have the part below the cut fall.
So an airplane at 25,000 would cause only about 25,000 feet to fall. It's like spinning a bucket on a rope. Cutting the Rope causes the bucket to fly out. Depending on the tension on the cable we might have trouble fixing the far end, but the massive counter weight could be fixed.
So a 5 mile no flyzone would work just fine.
Then I gotta bring up how you want this at a low latitude with lots of shipping. Dep

All they have to do is redesign the car/platform/etc a little bit to compensate.

And a small rocket would be a very small rocket, actually. we're talking hardly any more powerful than a few model rocket engines to counteract these forces.(think small thrusters or a tiny jet engine)

The "Space Elevators are unstable! The concept is doomed!" Slashdot summary would have been much more thrilling if there wasn't a link to the "Space Elevators are tricky! There might still need to be tiny final orbital adjustments!" New Scientist article, and even that would have been more exciting than the "Space Elevator dynamics is modeled by these stable but undamped equations! Sending multiple payloads up in the right phase causes the minor Coriolis-induced wobbles to cancel out!" Acta Astronautica article.

You people with your damn hyperlinks are ruining journalism. It's getting so a guy can't even wait breathlessly for the News At 11 anymore to find out what common household product might be Killing Our Children.

You people with your damn hyperlinks are ruining journalism. It's getting so a guy can't even wait breathlessly for the News At 11 anymore to find out what common household product might be Killing Our Children.

I know what you mean. Turns out it was steak knives. Anti-climactic for sure.

Of all of the technical and political roadblocks to building a space elevator, both of these seem quite minor in comparison. This is kind of like saying "I was going to bench press this Hummer H2, but since you added a fuzzy steering wheel cover it's going to be completely impossible now."

Corrolis force problems were one of the first things I thought of when I first heard about the space elevator, but I'd never seen the issue brought up.

It's a given that a elevator would be tethered at the equator, thus will be traveling at 1600kph, the velocity of geosynchronous orbit is what, 11000kph? Anything climbing from the bottom up will be accelerated to that as it ascends. So the question is how the hell do you mitigate this without literally bending the thing out of shape - burning fuel is silly It's not a trivial velocity, it's 40% of what would put you into LEO orbit anyway!

Despite this, I don't think this is a showstopper, remember Arthur C Clarke told is it will be built...

It's accelerated by the tension of the space elevator cable, which is attached to a large counterweight beyond geo-synch orbit. This causes the elevator cable to pull on the counterweight and on the Earth. Eventually the orbital energy comes from the rotation of the Earth, slowing it ever so slightly. The system naturally returns to a state where the elevator cable is perpendicular to the plane tangent to the earth's surface at the attachment point as the counterweight drifts back into a higher orbit via c

current nano-fiber technology has to improve by a couple orders of magnitude before we can even think about building such a cable

the costs for building the cable aren't even possible to estimate, and are likely to dwarf the cost of conventional rocket launch for the foreseeable future

the technology required to construct the climbers, moor the counterweight, produce and deploy the cable, provide power, etc, doesn't exist

"space management" issues such as collisions with space junk, aircraft, etc, are going to be difficult at best to resolve

and because the above factors, financial backing for such an enterprise is all but non-existent

... let's just say I wouldn't be holding my breath waiting for the space elevator. Unless we can solve the problems involving manufacturing of carbon fibers with the appropriate properties (which is far from a sure thing), worrying about issues like Coriolis on the ascending climbers is like discussing how many angels can dance on the head of a pin.

The system will need to send electrons to the surface constantly, creating a massive current on a 32,000 mile line. Even if you J-Hook the thing over the point and bring it back into the atmo, it is going to make a mess.

We are better off using this nano-reinforced material to either a) create a 1km wide column that is devoid of atmosphere (and hence no resistance) or b) create a 1km volume capable of containing vacuum, as per Diamond Age, creating the lightest possible lighter-than-air vehicles to SSTO.

Multiply the power generated by the many orders of magnitude that the elevator is longer than the tether was.

As the elevator swung through the magnetosphere on the aposol and perisol points of its rotation, it'd be generating billions of volts and conducting huge amounts of current down to the ground and out the top end of the elevator.

The ground equipment and probably a portion of the bottom of the elevator would be turned to plasma. Same at the other end. The rest of the structure would orbit free and crash. Enough of it would not be burned away that the remainder would wrap around the Earth several times.

Note that this scenario would require it be completely built before the effect started. This is, of course, impossible. It would be burning itself away as its length was increased. Note also that this is due to the structure only, not the dynamics of something going up and down it. Nothing would ever get the chance to make the trip.

It is at first obvious that generating power in this fashion would power the elevator. Less obvious but more important, is what to do with the 99.999% of the generated power that's surplus. It's just too much surplus, and we have no technology to carry that much power safely on such a structure.

Look at the details of the tether experiment. Less than 20 km of tether produced 3500 volts and burned the tether away from the shuttle. The elevator would be 4216 times longer. Also, the tether was not directly vertical, whereas the elevator would be. The amount of power generated would be more than the 4216 times the length.

A primary choice for the elevator structure is carbon fiber. When that stuff burns it puts out a cloud of random buckytube-like particles which pose a health hazard much like a cloud of equivalent mass of asbestos. The best choice of material for the structure would be pretty near the worst choice when it came to its inevitable self-destruction.

If the elevator burned away in the atmosphere, the carbon particulate would be a nasty pollutant. If the structure boiled itself away at higher altitude, outside the atmosphere, it would leave a trail of carbon particles that would become a hazard to spacecraft. Flying through that cloud would be like plowing into fine sand. A brief encounter would be very little trouble. But trying to fly at that same orbit for an extended time would erode away the spacecraft. If it were dense enough, it could also collect some charge in the manner of the tether, and discharge that into a spacecraft approaching it.

Not necessarily. You could place a big enough solar sail at the far end of the elevator arm to put the whole thing in tension, which would make it stable. That may be the only way to have a space elevator for Venus.

No matter what medium you are using for propulsion (Air, C02, or combusting fuel), it still requires the same amount of energy to make the stability corrections (in one case the energy comes from fuel combustion, in the other case, it comes from some sort of air pumps at the ground). The point is, that it still requires a potentially unknown amount of energy to stabilize the thing. Since the *point* of the space elevator idea is to conserve energy, the question becomes, will we actually conserve any energy

1) Space elevators do not lower the energy required - they just use the energy differently.2) They do not take you to where the gravity is weak - they take you to the point where the force of gravity (which is essentially unchanged) is balanced by centripetal force (which, being linked to w^2r goes up linearly with distance).3) Rockets typically take you to about 7.7 km/s (orbit), not 11.2km/s (escape).4) The energy given to the satellite (assuming the same final orbit) is identical regardless of the launch vehicle/elevator used. What is different is the energy efficiency of the system in putting energy into the satellite:

A rocket sends lightweight propellant in the opposite direction very fast in order to transfer the energy. An elevator sends a huge mass (essentially the entire earth) very slowly in the opposite direction. Since momentum is conserved, the mass x velocity of both systems is the same - but since the Earth masses a lot more than most rockets, the Earth's relative velocity is far lower. This is where the e=0.5*m*v^2 comes in - the "wasted" energy is the energy provided to the Earth or propellant. Earth has a small v, big m - which works better than the rockets big v little m.

So you always have to give the satellite the same energy - there are just different efficiencies of giving it that energy. Space cannons have the problem of needing to give that energy extremely quickly... very difficult indeed.

Earth's gravity is substantially weaker at GSO. GSO altitude is large compared to the Earth's radius.

Space elevators *do* lower the energy that is supplied by the launch system.In a space elevator, the energy for the sideways motion comes from the rotation of the Earth (hence the Coriolis forces on the elevator mentioned in the summary). For GSO, that's less than the energy spent climbing up the gravity well, but it's still not trivial.

For escape trajectories, the elevator looks even more attractive -- once you pass GSO, the ride becomes free, and you gain energy from the dynamics of the system without spending any propellant / electricity / whatever. Time it carefully, and you just "fall" off the end of the cable on the right trajectory.

All of that said, rockets aren't *that* inefficient. For LEO, they can be 10% efficient or better (slightly worse for GSO). That's not great, but there are no proposed methods of getting energy to the elevator car that are all that efficient either, especially when you count electricity generation losses. Given the disparity in capital costs, and the fact that in neither case is the energy cost a noticeable fraction of the budget, I suspect rockets will win out for some time to come...

A concern with talking about the efficiency of rockets is that you have to carefully define what you mean: normal chemical rockets have extremely high Carnot efficiencies, mediocre mass and energy efficiencies. A space elevator doesn't have a Carnot efficiency, has terrible mass efficiency, but extremely good energy efficiency. An ion thruster has no Carnot efficiency, has great mass efficiency, and terrible energy efficiency.

Now consider something like a gaseous-core nuclear rocket (fission, with the core